The present invention relates to a washings weight detection and a washing operation control system for use in an electric washing machine and, more particularly, to an apparatus for use in an electric washing machine which can wash clothes and spin-dry them, for detecting a washings weight, i.e., an amount of clothes and controlling the washing operation in accordance with the detected weight.
Some conventional electric washing machines, which can wash clothes and also spin-dry them, detect a washings weight and use detected data for controlling the washing operation and the like. An example of washings weight detection apparatus for use in such electric washing machines is a capacitive or differential transformer type weight sensor provided at a tub suspending mechanism and the like of an electric washing machine. An electrical quantity, such as a capacitance or inductance generated by the weight sensor, is converted into a frequency by an oscillator. The washings weight is determined in accordance with the frequency.
However, the weight sensor may have mechanical errors made during the manufacture, or may be located in an inappropriate position. For this reason, the accuracy of the washings weight detected by the sensor may be insufficient. Consequently, the accuracy of clothes amount detection may be low.
Another type of a weight sensor is known which detects an electrical value such as the input current of a motor, which varies in accordance with the load acting on the motor driving a rotary tub and an agitator during the washing operation of an electric washing machine, and determines the washings weight from the detected electrical value.
Since this sensor is purely electrical, the load acting on the motor can be correctly detected. However, since the load is detected while clothes are being washed, the relationship between the load and actual washings weight cannot accurately be determined. As a result, the accuracy of washings weight detection is low. That is, at an initial period of washing operation, the clothes in a rotary tub often float on a water surface. Therefore, the clothes do not act on the motor as a load. Moreover, since the clothes irregularly move with respect to the agitator during the washing, the load of the motor irregularly and largely varies. Under such circumstances, the washings weight does not always correspond to the load of the motor. Therefore, even if the load is accurately detected, the washings weight cannot be accurately determined from the detected load.
Therefore, the data detected by the conventional washings weight detection apparatus is not always satisfactory. As a result, the washing operation control cannot be performed well.